For some time, the ability to perform experiments requiring the presentation of high level, wide band, minimum distortion sounds to the eardrum of guinea pigs has been unduly restricted by presently available small electroacoustical transducers suitable for earbar interface. As a result, high level sounds have had to be produced from loudspeakers mounted some distance from the ear (field stimulation). As a result, distortion, maximum achievable level and accuracy of measurement suffer. The availability of electroacoustic transducers operated into closed systems (earbar or ear canal) and capable of producing very high levels would allow one time acute exposures at levels sufficient to cause immediate auditory damage resulting in significant time savings. In addition, the pseudorandom noise which will serve as stimulus in some experiments, is characterized by a line spectrum. Prevention of distortion in line spectrums is particularly important. There have been reports in the high fidelity literature of earphone transducers having many of the desirable characteristics, so an attempt will be made to have such a device optimized for closed system applications.